This invention relates generally systems for identifying currency, and more particularly to an improved process for identifying a genuine currency note. The increased usage of vending machines, money changers, bank terminal machines etc in recent years has made it necessary to automatically and correctly identify the authenticity of currency notes, and especially bank notes.
The identification of the currency notes is generally done by detecting light reflected from the notes, as described in U.S. Pat. No. 4,179,685. Merely detecting reflected light, however, has the disadvantage of failing to verify the authenticity of the detected note to prevent the acceptance of forged notes. One method which has been developed to verify authenticity by detecting magnetic material, metallic element, or color which is contained in the currency or its printing ink is disclosed in Japanese patent disclosure Nos. 54-4199 and 53-146698 corresponding to United States patent application Ser. No. 969,379, filed Dec. 14, 1978. In these disclosures, the detection of color, magnetic material, or metallic elements is performed by substantially the same process.
For example, in the Japanese patent disclosure No. 54-4199, the analogue detecting signal S.sub.a, as shown in FIG. 1A, is obtained by scanning a detected bank note and compared with an analogue standard signal S.sub.f, corresponding to a genuine note, to obtain an absolute difference signal S.sub.g (see FIG. 1B). If difference signal S.sub.g remains less, during its entire time interval, than a predetermined level V.sub.a, then the detected bank note is considered to be genuine.
If at any instant the difference signal exceeds level V.sub.a, the note will be rejected. This method, therefore has disadvantages in that a note having a minor disfigurement due to its handling (i.e., wrinkles) and daily processing will be rejected which otherwise should not occur. These minor disfigurements can be caused by handling which stretch, shrink, and/or fade printing patterns or which decrease the quantity of magnetic material or metallic elements.
In the field of currency identification systems, the printing patterns of the detected objects (i.e. currency notes) are in fixed and standard forms; as a result, the measured difference between the detected note and signals corresponding to a genuine note are generally small. On the other hand, in the field of pattern recognition systems the printing patterns are generally not in fixed and standard forms; variations in the figures or patterns exist which must be recognized and checked for comparison. As a result, the systems circuitry must be sensitive to greater differences between the detected pattern and the known pattern, than is the case with currency note identification systems where greater differences are not tolerated. In the field of pattern recognition, methods are utilized which calculate numerous values of similarity between areas of a detected object and corresponding areas of known object to determine if the detected pattern should be accepted (See U.S. Pat. Nos. 3,688,267 and 3,906,446). This instant invention incorporates same features of pattern recognition to a currency note identification system whereby a novel method and apparatus is employed to calculate a value of similarity between a detected note and a genuine note to determine authenticity. The disadvantages resulting from utilizing the prior art method of comparing an absolute value difference signal to a predetermined level V.sub.a is avoided. Moreover, the time consuming disadvantage of prior art pattern recognition systems of calculating a large number of values of similarity between numerous areas of a detected pattern and corresponding areas of a known pattern is eliminated. The instant invention utilizes pattern recognition techniques wherein, however, a value of similarity between the detected note and the genuine note is employed, rather than numerous values.